At Wed, 31 Oct 2012 23:06:39 -0400, Harry Spier wrote: > Dear list members, > > I see from the Racket Drawing Toolkit documentation that there are > monochrome bitmaps but I'm not clear from the documentation how to > access and manipulate these monochrome bitmaps. > > Specifically: > 1) If I load a bitmap with a greyscale image file using the form: > (make-object bitmap% > in ;path to monochrome image files > [ kind > bg-color > complain-on-failure?]) > > Will that create a monochrome bitmap from the greyscale image?
Yes, if the file format is PNG or XBM, but other file formats always load into color bitmaps. > If > not is there another way to load a file as a monochrome bitmap? After loading any kind of bitmap, you can create a same-sized monochrome bitmap and then draw a color bitmap into the monochrome one using `draw-bitmap' (after creating a `bitmap-dc%' to draw into the monochrome bitmap). > 2) How do I access pixel intensities from a monochrome bitmap? > The documentation for get-argb-pixels says it copies rgb values plus > alpha channel into pixels. For a monochrome bitmap is it the alpha > channel which holds the pixel intensity where 1 is black and 0 is > white? The same pixel intensities are used as for color bitmaps: white is 255,255,255 and black is 0,0,0. A monocrhome bitmap doesn't have an alpha channel, but it you ask for its pixels in `just-alpha?' mode, then while pixels generate a 0 alpha and black pixels generate a 255 alpha. ____________________ Racket Users list: http://lists.racket-lang.org/users
